Piazzi

Piazzi, Giuseppe

ACHIEVEMENT(S): Discovered and named the first asteroid Ceres.

NICKNAME/ALIAS: None

DATE/PLACE OF BIRTH: 16 July 1746, at Ponte di Valtellina, Lombardy, Italy

[now Switzerland]

DATE/PLACE/AGE AT DEATH: 22 July 1826, in Naples, Italy. Aged 80

DISCIPLINE: Astronomer

FIELD: Astronomy

LANGUAGE: Italian

PARENTS: ?

SIBLINGS: ?

SPOUSE: None

CHILDREN: None

EDUCATION: 1764-1769, by the Theatine religious order

MAJOR WORK: 'Della scoperta del nuovo pianeta "Cerere Ferdinandea"', 1802

LIFE AND TIMES: From 1769, for ten years, Piazzi worked as a philosophy teacher in Genoa and a mathematics teacher at the new University of Malta. In 1779, he was made a professor of dogmatic theology in Rome, a colleague being Chiaramonti, who later became Pius VII.

The following year he was appointed Professor of Higher Mathematics at the Palermo Academy in Sicily and put in charge of setting up an observatory there.

In 1787 Piazzi travelled to foreign observatories for advice and equipment, first to Paris, France to study with Joseph Lalande, and then, in 1788, to London, England, where he met such great astronomers as William Herschel*, Maskeleyne*, and the famous instrument-maker Ramsden*. Here, Piazzi studied Herschel's large telescopes and, with Maskelyne observed at Greenwich the solar eclipse of 3 June 1788.

While in London Piazzi commissioned from Ramsden a 5-foot vertical circle with reading microscopes for measuring star positions. This, plus a transit and other apparatus, was sent to Palermo in 1789 and installed in the new observatory in the Santa Ninfa tower of the royal palace of Palermo, where it remains to this day. The Palermo Observatory was opened in 1790 and Piazzi remained its Director until his death.

At Palermo, in May 1791, Piazzi began observations for his great project of mapping the positions of the fixed stars by their precise astronomical coordinates. Palermo was then the southernmost observatory in Europe and enjoyed a favourable climate, and these conditions, together with the quality of his new equipment, enabled Piazzi to produce new and more accurate measurements than had previously been achieved.

During the course of his observations, on 1 January 1801, Piazzi was examining the apparent "gap" in the Solar System between Mars and Jupiter, which had long been a source of speculation for astronomers (see Bode), when he detected a faint new body. Piazzi continued to observe the new body over a geocentric arc of only 3[degrees] for six

weeks (until 11 February, when it could no longer be detected because of its position in relation to the Sun).

He decided from its movement that it must be a planet or a comet. Piazzi sent his findings almost immediately to Barnaba Oriani, director of the Brera observatory in Milan, and to Bode*, director of the Berlin Observatory, and published them.

The importance of Piazzi's findings lay in the fact that, if the new body were a planet, it might be possible to calculate its circular orbit from Piazzi's limited observations, as in the case of Uranus, even if the arc of the (presumably elliptical) orbit were to prove short. Using Piazzi's data, in December 1801 the German scientist Gauss* developed a new method for calculating the orbit of the body from so few observations, and sent his prediction to Zach* of the Gotha Observatory.

The celestial body was rediscovered, using Gauss's predictions, in almost exactly the position that Gauss had predicted, by Olbers*. This proved that the body was in fact a planet, and in a paper of 1802, 'Della scoperta del nuovo pianeta "Cerere Ferdinandea"', Piazzi named it both for Ceres, the patron goddess of Sicily, and his patron, Ferdinand I.

However, the dimness of this "planet", considering its distance from the Earth, indicated that it was very small, and this led Piazzi into a disagreement with William Herschel. In May 1802 Herschel calculated that Ceres was only 320 km in diameter (it is now known to have a diameter of about 440 miles (700 km), and revolves around the Sun in 4.6 terrestrial years) and, in a letter to Piazzi, he argued that did not warrant being called a planet.

He proposed the name "asteroid" since it is intermingled with and similar to the small fixed stars. Herschel went on to suggest three forms of celestial bodies: planets, asteroids and comets. The term "asteroid" became popular, although by the late 20th century Piazzi's term "minor planet" had again become standard.

The discovery alsoinitiated another controversy, this time in Germany between astronomers, in particular Zach, and the young philosopher Hegel*, who had just published a dissertation arguing that there were only seven planets in the solar system.

Meanwhile, Piazzi had, since 1792, continued to make precise measurements of star coordinates, and after ten years published in 1803 a catalogue of the positions of 6,748 stars. This catalogue was far more accurate than any of its predecessors.

In 1813 he published a second catalogue which gave the position of 7,646 stars. Piazzi was helped in the proofreading of his star catalogue by an ex-naval officer, William Henry Smyth, who was also an amateur astronomer and archaeologist, who in 1819 named his son Piazzi Smyth* (he would become Astronomer Royal for Scotland from 1844-1888).

In March 1817 Piazzi was summoned to Naples to supervise the completion of the observatory already under construction on the hill at Capodimonte, which had begun under the direction of Joachim Murat. As Piazzi was unwilling to leave Palermo, the King then appointed him director-general of both observatories (in Palermo and Naples)

His health having weakened, Piazzi settled in Naples in 1824, and in the same year he was elected as president of the Neapolitan Academy of Sciences.

ASSESSMENT: He made a major contribution to knowledge of the solar system.

EXTRA CONNECTIONS: His work related to that of Sir John Frederick William Herschel* and Struve*

ONELINER: Giuseppe Piazzi, who discovered the first asteroid

BIBLIOGRAPHY:

DSB

Biographical Dictionary of Astronomers